Arduino LCD: LiquidCrystal_I2C library

A LiquidCrystal LCD (Liquid Crystal Display) can be used in two ways:

• The normal way, with a lot of outputs (6) and wires (10).
• The I2C-way, with only 2 data-lines (SDA and SCL) and 2 powerlines (+5V, GND).

1. The normal way, with a lot of outputs (6) and wires (10).
   Here you can find some good explanation:
   http://arduinoliquidcrystal.readthedocs.org/en/latest/liquidcrystal.html
   
   The library for this is “LiquidCrystal.h” and that library is part of the Arduino-ide.
   All functions are explained on the website above.

   // include the library code:
   #include <LiquidCrystal.h>
   
   // initialize the library with the numbers of the interface pins
   // LCD-ports      RS   E  D4 D5 D6 D7
   LiquidCrystal lcd(12, 11, 5, 4, 3, 2);
   
   void setup() {
     // set up the LCD's number of columns and rows: 
     lcd.begin(16, 2);
     // Print a message to the LCD.
     lcd.print("hello, world!");
   }
   
   void loop() {
     // Turn off the blinking cursor:
     lcd.noBlink();
     delay(3000);
      // Turn on the blinking cursor:
     lcd.blink();
     delay(3000);
   }
   

2. The I2C-way, with only 2 data-lines (SDA, the data-line and SCL, the clock-line) and 2 powerlines (+5V, GND).
   For this we need to use a ‘IO expander’ like this:
   
   You can connect multiple devices on the I2C-bus, each device gets an address:
   – 0x20 = 0010 0000,
   – 0x21 = 0010 0001,
   – 0x22 = 0010 0010,
   – …
   You can address 128 devices (= 7bit addressing), from 0 to 127).
   This site explains the inner working of the I2C-protocol:
   http://www.robot-electronics.co.uk/acatalog/I2C_Tutorial.htmlManufacturers gives these addresses to there I2C-devices.
   If the chip on your board is a PCF8574T, then the I2C-addresses can lay in the range of  0x20 to 0x27.
   If the chip on your board is a PCF8574AT, then the I2C-addresses can lay in the range of 0x3F to 0x38.
   This IO-module has a default I2C-address of 0x27, but you can change it yourself by changing the jumpers A0, A1 and A2 on the board (MARK the reverse order of A0A1A2 => A0A1A2).
   E.g. For PCF8574T: A2-A1-A0 or 001 or 0x26

   A2A1A0 (PCF8574T)
   000 = 0x27    011 = 0x24   110 = 0x21
   001 = 0x26    100 = 0x23   111 = 0x20
   010 = 0x25    101 = 0x22

   E.g. For PCF8574AT: A2-A1-A0 or 001 or 0x3E

   A2A1A0 (PCF8574AT)
   000 = 0x3F    011 = 0x3C   110 = 0x39
   001 = 0x3E    100 = 0x3B   111 = 0x38
   010 = 0x3D    101 = 0x3A

1. 
   In this picture you see that ‘jumper A0’ is soldered.
   So the I2C-address for this module is 0x26 or 0x3E.
   
   (source: https://forum.micropython.org/viewtopic.php?f=14&p=19249)

1. The library , called “LiquidCrystal_I2C.h“, needed for these modules to work, can be found here:
   https://github.com/marcoschwartz/LiquidCrystal_I2CAlways check first if libraries aren’t available in the arduino-ide, before you download them.(Mark! Github always add ‘-master’ when you download a zip-file, unzip, rename the directory without ‘-master’, zip again and import the zip in arduino-ide)
2. In the following example-code, there are 2 I2C-modules used with 2 different LCD-displays (16×2 and 20×4 display), also found partly in the LiquidCrystal_V1.2.1.zip.

You also need the ‘Wire’-library.

 

It can be used with the same functions as in “LiquidCrystal”, only initialisation of the LCD-object is different.

LiquidCrystal_I2C lcd1(0x20,16,2); // set the LCD address of the first lcd to 0x20
                                   // for a 16 chars and 2 line display

#include <Wire.h> 
#include <LiquidCrystal_I2C.h>

// library for the 'mjkds'-module
// http://hmario.home.xs4all.nl/arduino/LiquidCrystal_I2C/
LiquidCrystal_I2C lcd(0x20,16,4); // set the LCD address of the first lcd to 0x20
                                  // for a 16 chars and 4 line display
 
void setup()
{
 lcd.init(); // initialize the first lcd 
 
 // Print a message on the first LCD.
 lcd.backlight();
 lcd.print("Hello, world 0!");
 lcd.setCursor(1, 1);
 lcd.print("Hello, world 1!");
 lcd.setCursor(2, 2);
 lcd.print("Hello, world 2!");
 lcd.setCursor(3, 3);
 lcd.print("Hello, world 3!");
}  // end setup
 
void loop()
{
} // end loop

Connecting your I2C-module to an Arduino via SDA and SCL

Found here (http://tronixstuff.com/2014/12/01/tutorial-using-ds1307-and-ds3231-real-time-clock-modules-with-arduino/)

Both modules use the I2C bus, which makes connection very easy.

Moving on – first you will need to identify which pins on your Arduino or compatible boards are used for the I2C bus – these will be knows as SDA (or data) and SCL (or clock).

On Arduino Uno or compatible boards, these pins are A4 and A5 for data and clock:

If you’re using an Arduino Mega the pins are D20 and D21 for data and clock:

If you’re using an Pro Mini-compatible the pins are A4 and A5 for data and clock, which are parallel to the main pins, as shown below:

Other I2C-modules are available, like the ‘mjkds’-module:

The library to use for this ‘mjkdz’-module is “LiquidCrystal_I2C.h” and can be found here:
http://hmario.home.xs4all.nl/arduino/LiquidCrystal_I2C/
Mark the same name for the library, but initialisation is a bit different.

The following code is not compatible with the above chips PCF8574AT and PCF8574T!

#include <Wire.h> 
// Use this library with I2C-module found on the webpage
// http://4tronix.co.uk/arduino/I2C_LCD_Module.php
#include <LiquidCrystal_I2C.h>


// set the LCD address to 0x27 for a 20 chars 4 line display
// Set the pins on the I2C chip used for LCD connections:
// addr, en,rw,rs,d4,d5,d6,d7,bl,blpol
LiquidCrystal_I2C lcd1(0x27, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE); // Set the LCD I2C address
LiquidCrystal_I2C lcd2(0x26, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE); // Set the LCD I2C address

void setup()
{
 lcd1.begin(16,2); // initialize the lcd
 lcd2.begin(20,4); // initialize the lcd
 // Print a message to the LCD.
 lcd1.backlight();
 lcd1.print("hello, world 0!");
 lcd1.setCursor(1, 1);
 lcd1.print("hello, world 1!");
// lcd1.setCursor(2, 2);
// lcd1.print("Hello, world 2!");
// lcd1.setCursor(3, 3);
// lcd1.print("Hello, world 3!");


 lcd2.backlight();
 lcd2.print("HELLO, WORLD 0!");
 lcd2.setCursor(1, 1);
 lcd2.print("HELLO, WORLD 1!");
 lcd2.setCursor(2, 2);
 lcd2.print("HELLO, WORLD 2!");
 lcd2.setCursor(3, 3);
 lcd2.print("HELLO, WORLD 3!");
}

void loop()
{
}